Hitherto there has been disclosed an SBE (Supertwisted Birefringence Effect) type liquid crystal display device which is known as a liquid crystal display device capable of displaying a large amount of data at high luminance contrast in multiplex driving at a high duty ratio.
The SBE type liquid crystal display device, however, has a disadvantage that an image area as well as a background area is liable to be tinted with a specific color because a birefringence effect is utilized, and this disadvantage causes the problems of: (1) poor quality image, (2) no flexibility to meet the colors appointed by users, and (3) difficulty in displaying a color image.
To solve such a tinting problem and provide distinct monochromatic displaying, the following techniques have been hitherto proposed;
(1) OMI technique where in order to prevent tinting, the product, .DELTA.n.multidot.d, of a refractive anisotropy, .DELTA.n, of a liquid crystal and a thickness, d (.mu.m), of a liquid crystal layer is adjusted to 0.4 to 0.6 .mu.m (Appl. Phys. Lett. 50 (1987) pp. 236-238);
(2) a double-layer cell technique where one liquid crystal cell is superposed on another liquid crystal cell containing a reversely twisted alignment of liquid crystal molecules in a liquid crystal layer to form a double-cell structure, and the another liquid crystal cell is used as an optical compensator in order to prevent tinting (Nikkei Micro-Device, Oct. 1987, pp.84-88).
However, the foregoing OMI technique (1) has the problems; a high luminance contrast is not attained; a displayed image is dark; and positive prevention of tinting is difficult.
The double-layer cell technique (2) has also the problems; a manufacturing cost and a weight of the device are more than those of the device composed of a single liquid crystal cell; and because of difficulty to make thicknesses of two liquid crystal cells uniform, a liquid crystal cell fails to fully function as an optical compensator, so that it is difficult to completely prevent tinting.
Further, luminance contrast is dependent on an average tilt angle .theta..sup.ON of liquid crystal molecules, and the average tilt angle increases with an angle .theta..sub.0 (pretilt angle) made by an electrode substrate and a director of the liquid crystal molecules which are in contact with the electrode substrate. The angle .theta..sub.0 is settled when an alignment layer is formed. A conventional alignment layer is formed by a rubbing technique, and the pretilt angle .theta..sub.0 is usually about 10.degree., or at most 25.degree.; however, the pretilt angle .theta..sub.0 of such level does not contribute to achieving preferable luminance contrast of not less than 50.